For what it's worth Anthropic explicity denies that. "To state it plainly: We never reduce model quality due to demand, time of day, or server load"

Also can see https://marginlab.ai/trackers/claude-code/

It's very interesting to me how widespread this conception is. Maybe it's as simple as LLM productivity degrading over time within a project, as slop compounds.

Or more recently since they added a 1m context window, maybe people are more reckless with context usage